In many ways, American attitudes toward the conflict between Israel and the Palestinians haven't changed at all in 40 years. But in other ways, attitudes toward this intractable Mideast conflict have changed radically.

On the surface, aggregate public opinion has been remarkably stable since 1978, with overall sympathy for the two sides in the conflict barely changing at all. Forty-five percent of Americans sided with Israel then and 46 percent do now. Likewise, 14 percent favored the Palestinians in the late 1970s, while 16 percent take that position today.

But the consistency of the aggregate numbers conceals a chasm opening up beneath the surface, with Republicans and Democrats moving in polar-opposite directions. Where 49 percent of Republicans sided with Israel in 1978, an astounding 79 percent do now. The percentage of Democrats supporting Israel, meanwhile, has fallen from 44 to 27 percent.

What was once a mere five percentage-point difference between the parties over support for Israel is now a 52-point rift.

The partisan polarization that's produced a hollowing out of the ideological center in American public life on a growing number of issues has now reached the politics of the Middle East. The practical consequences are unlikely to be pretty.

For one thing, the growing gap between the parties opens the prospect of wild swings in policy from administration to administration. With the GOP's military hawks and millenarian evangelicals firmly committed to defending the Jewish state regardless of its actions in the West Bank and Gaza Strip, Republican presidents will be increasingly likely to follow President Trump's lead in siding unconditionally and unambivalently with Israel in its conflict with the Palestinians.

Critics of American policy in the Middle East have long accused the U.S. of doing precisely that, but the reality is that as recently as the administration of George W. Bush, Republican presidents aimed to be seen as honest brokers attempting to steer the parties toward a lasting peace in the form of a two-state solution. That's one reason why Bush refrained for eight years from moving the U.S. embassy to Jerusalem — because he and his advisers thought that this purely symbolic act would needlessly (and understandably) antagonize the Palestinians, thereby decreasing American leverage in future negotiations over a resolution of the conflict.

President Trump's decision to break from Bush's policy (which President Obama also upheld) and relocate the embassy reflects the administration's abandonment of any pretense to fairness in the conflict — a change that was made possible by the lopsided support Israel enjoys among Republican voters.

What happens the next time a Democrat wins the White House, bringing drastically different views to the Oval Office? President Obama gave us a tentative and halting taste of what we will see — namely, the effort (during Obama's first term) to use our leverage to get Israel to slow or halt the growth of settlements on occupied and contested land. Such demands will likely intensify under a future Democratic president, perhaps growing to include taking a stand against Israel at the United Nations or decreasing the amount of military aid it receives. Coming after the Trump administration's unprecedented embrace of the Jewish state, the shift in approach will be jarring, to say the least. Especially since it will surely be followed, in turn, by a future Republican president who radically shifts course once again.

But this assumes that the Democratic Party's lurch to the left on Israel will precisely mirror the GOP's lurch to the right, and that is far from clear. While the Democrats have indeed become less supportive of Israel overall, the extent of the shift varies quite a lot across the ideological spectrum within the party. Whereas 35 percent of conservative and moderate Democrats continue to sympathize with Israel over the Palestinians, for liberal Democrats the percentage drops to 19 percent. Meanwhile, nearly twice as many liberals (35 percent) sympathize more with the Palestinians.

That's a picture of a party sharply divided. Whichever way it moves — moderating slightly in comparison to the stridently pro-Israel line of the Republicans or diverging drastically from it to please the party's increasingly anti-Israel liberal base — Democrats will face angry dissension in their ranks.

With the gap between the parties — and within the Democratic Party — growing ever-wider on the issue, get ready for the Israeli-Palestinian conflict to erupt in electoral form within the American political system. Add it to the lengthening list of issues on which finding common ground and consensus eludes us as a nation.